This invention generally relates to power supplies and more particularly to a DC to DC converter employing a push-pull oscillator.
DC to DC converters are well known and operate to convert an available DC input voltage to a DC output voltage or multiple output voltages with isolation between the input and the output. Such converters normally utilize high frequency switching techniques to enable one to achieve small transformer size which, in turn, provides isolation and voltage scaling. There are many different types of converters each having specific advantages and disadvantages. For example, square wave inverter stages may be used where the secondary voltage of a transformer is rectified and filtered to provide a desired DC output. With the square wave inverter the output voltage is not regulated and is a function of the input voltage and load current. However, for fixed input voltages and fixed loads, the output voltage may be maintained to a desired voltage tolerance. Where voltage output regulation is required due to input voltage and output load variations, regulation is conveniently achieved by pulse width modulation which controls the conduction period or duty cycle of an active device. As indicated a DC input source may be employed but most frequently a rectified and filtered AC input source serves as the DC source as in the case of off-line switch mode power supplies. Low power converters typically employ bipolar transistors or MOSFETs while very high power converters normally employ SCRs as switching elements. Each different approach has certain advantages. In the prior art it has been known, for example, to employ a free-running oscillator or a free-running circuit configuration to convert the DC voltage to an AC voltage which AC voltage is then rectified to produce a final output DC voltage. The term "free-running converter" implies that the operation of the converter is controlled by volt-second parameters of magnetic components. The switching frequency and the output voltage vary as a function of input voltage and load current. These converters are ideal for low power requirements and for operation from a fixed voltage source and into a fixed load. Essentially the prior art employed various free-running configurations to implement such converters including blocking oscillators and other circuit configurations. For examples of typical converter operation reference is made to a text entitled PRINCIPLES OF SOLID STATE POWER CONVERSION by Ralph E. Tarter (1985) published by Howard W. Sams & Company, Inc. As one can ascertain, while DC to DC converters are well known, there are many problems associated with each different approach and such problems have to be resolved accordingly. These problems relate to regulation of the output voltage, the amount of ripple, volumetric size, as well as the overall economics.
It is therefore an object of the present invention to provide a compact DC output voltage source having a regulated output voltage including low ripple.
It is a further object of the present invention to provide a regulated output DC voltage source having low ripple, small size, and which is relatively inexpensive to produce.